1. Field of the Invention
The present invention relates generally to a CDMA mobile communication system, and in particular, to an apparatus and method for gated transmission that assigns channels and does not require a separate resynchronization process.
2. Description of the Related Art
A conventional CDMA (Code Division Multiple Access) mobile communication system primarily provides voice services. However, the future CDMA mobile communication system will support the IMT-2000 standard, which provides a high-speed data service as well as the voice service. More specifically, the IMT-2000 standard provides a high-quality voice service, a moving picture service, and an Internet search service.
In a mobile communication system, a data communication service typically alternates between a transmission of burst data period and a long non-transmission periods. The bursts of data are referred to as “packets” or “packages” of data. In the next generation communication systems, traffic data is transmitted over a dedicated traffic channel for a data transmission duration, and the dedicated traffic channel is maintained for a predetermined time even when a base station and a mobile station have no traffic data to transmit. The mobile communication system transmits the traffic data over the dedicated traffic channel for the data transmission duration and maintains the dedicated traffic channel between the base station and the mobile station for a predetermined time even when there is no traffic data to transmit in order to minimize a time delay due to sync reacquisition when there is traffic data to transmit.
The invention will be described with reference to a UTRA (UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access) mobile communication system. Such a mobile communication system requires many states according to channel assignment circumstances and the existence/nonexistence of state information in order to provide a packet data service as well as a voice service.
FIG. 1A shows state transition in the cell connected state of the mobile communication system. Referring to FIG. 1A, the cell connected state includes a paging channel (PCH) state, a random access channel (RACH)/downlink shared channel (DSCH) state, a RACH/forward link access channel (FACH) state, and a dedicated channel (DCH)/DCH, DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl (Control Channel) state.
FIG. 1B shows a user data active substate and a control-only substate of the DCH/DCH, DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl state. It should be noted that the novel gated transmission device and method is applied to a state where there is no traffic data to transmit for a predetermined time (e.g., DCH/DCH control-only substate).
The existing CDMA mobile communication system which mainly provides the voice service releases a channel after completion of data transmission and connects the channel again when there is further data to transmit. However, in providing the packet data service as well as the voice service, the conventional data transmission method has many delaying factors such as a reconnection delay, thus making it difficult to provide a high-quality service. Therefore, to provide the packet data service as well as the voice service, an improved data transmission method is required. For example, in many cases, data transmission is performed intermittently for Internet access and file downloading. Thus, there are transmission and non-transmission periods. During the non-transmission period, the conventional data transmission method releases or maintains the traffic (or data) channel(DPDCH OR DSCH) and associated control channel(DPCCH). Releasing the traffic channel and associated control channel require a long time to reconnect the channels, and maintaining the traffic channel and associated control channel waste the channel resources.
A downlink (or forward link) for transmitting signals from the base station to the mobile station or an uplink (or reverse link) for transmitting signals from the mobile station to the base station includes the following physical channels. The physical channels include a dedicated physical control channel (hereinafter, referred to as DPCCH) in which pilot symbols are included for sync acquisition and channel estimation, and a dedicated physical data channel (hereinafter, referred to as DPDCH) for exchanging traffic data with a specific mobile station. The downlink DPDCH includes the traffic data, and the downlink DPCCH includes, at each slot (or power control group), transport format combination indicator (hereinafter, referred to as TFCI) which is information about the format of transmission data, transmit power control (hereinafter, referred to as TPC) information which is a power control command, and control information such as the pilot symbols for providing a reference phase so that a receiver (the base station or the mobile station) can compensate the phase. The DPDCH and the DPCCH are time multiplexed within one power control group and the DPDCH and DPCCH signals are spread with one orthogonal code in downlink, and DPDCH and DPCCH signals are separated by using different orthogonal codes in the uplink.
For reference, the invention will be described with reference to a case where a frame length is 10 msec and each frame includes 16 or 15 power control groups (PCGs), i.e., each power control group has a length of 0.625 msec or 0.667 msec. It will be assumed herein that the power control group (0.625 msec or 0.667 ms) has the same time period as the slot (0.625 msec or 0.667 ms). The power control group (or slot) is comprised of pilot symbol, traffic data, transmission data format concerning information TFCI, and power control information TPC. The values stated above are given by way of example only.
FIG. 2A shows a slot structure including the downlink DPDCH and DPCCH. In FIG. 2A, although the DPDCH is divided into traffic data 1 and traffic data 2, there is a case where the traffic data 1 does not exist and only the traffic data 2 exists according to the types of the traffic data. Table 1 below shows the symbols constituting the downlink DPDCH/DPCCH fields, wherein the number of TFCI, TPC and pilot bits in each slot can vary according to a data rate and a spreading factor.
Unlike the downlink DPDCH and DPCCH, uplink DPDCH and DPCCH for transmitting signals from the mobile station to the base station are separated by channel separation codes.
FIG. 2B shows a slot structure including the uplink DPDCH and DPCCH. In FIG. 2B, the number of TFCI, FBI (FeedBack Information), TPC and pilot bits can vary according to the circumstances influencing the type of the traffic data, such as a provided service, transmit antenna diversity, or a handover (or handoff). The FBI is information about two antennas that the mobile station requests, when the base station uses transmit diversity antennas. Tables 2 and 3 below show the symbols constituting the uplink DPDCH and DPCCH fields, respectively.
TABLE 1Downlink DPDCH/DPCCH FieldsChannelChannelSymbolDPDCHDPCCHBit RateRateBits/FrameBits/SlotBits/Slot(kbps)(ksps)SFDPDCHDPCCHTOTBits/SlotNdata1Ndata2NTFCINTPCNpilot16851264961601022024168512321281601002224321625616016032020280283216256128192320200822864321284801606404062402864321284481926404042422812864641120160128080145602812864649922881280806568282561283224001602560160301200282561283222722882560160221208285122561648322885120320622400216512256164704416512032054240821610245128995228810240640126496021610245128982441610240640118496821620481024420192288204801280254100802162048102442006441620480128024610088216
TABLE 2Uplink DPDCH FieldsChannelChannel Bit RateSymbol(kbps)Rate (ksps)SFBits/FrameBits/SlotNdata1616256160101032321283202020646464640404012812832128080802562561625601601605125128512032032010241024410240640640
TABLE 3Uplink DPCCH FieldsChannelChannel BitSymbolRate (kbps)Rate (ksps)SFBits/FrameBits/SlotNpilotNTPCNTFCINFBI161625616010622016162561601082001616256160105221161625616010720116162561601062021616256160105122
Tables 1 to 3 show an example where one DPDCH is a traffic channel. However, there may exist second, third and fourth DPDCHs according to the service types. Further, the downlink and uplink both may include several DPDCHs. Here, SF indicates a Spreading Factor.
A hardware structure of the conventional mobile communication system (base station transmitter and mobile station transmitter) will be described below with reference to FIGS. 3A and 3B. Although the base station transmitter and mobile station transmitter will be described with reference to three DPDCHs, the number of DPDCHs is not limited.
FIG. 3A shows a structure of the conventional base station transmitter. Referring to FIG. 3A, multiplier 111 multiply a DPCCH signal by gain coefficient G1, multipliers 121, 131 and 132 multiply DPDCH1, DPDCH2 and DPDCH3 signals, which have undergone channel encoding and interleaving, by gain coefficients G2, G3 and G4, respectively. The gain coefficients G1, G2, G3 and G4 may have different values according to circumstances such as the service option and the handover. A multiplexer (MUX) 112 time-multiplexes the DPCCH signal and the DPDCH1, signal into the slot structure of FIG. 2A. A first serial-to-parallel (S/P) converter 113 distributes the output of the multiplexer 112 to an I channel and a Q channel. Second and third S/P converters 133 and 134 S/P-convert the DPDCH2 and DPDCH3 signals and distribute them to the I channel and the Q channel, respectively. The S/P converted I and Q channel signals are multiplied by channelization codes Cch1, Cch2 and Cch3 in multipliers 114, 122, 135, 136, 137 and 138, for spreading and channel separation. Orthogonal codes are used for the channelization codes. The I and Q channel signals multiplied by the channelization codes in the multipliers 114, 122, 135, 136, 137 and 138 are summed by first and second summers 115 and 123, respectively. That is, the I channel signals are summed by the first summer 115, and the Q channel signals are summed by the second summer 123. The output of the second summer 123 is phase shifted by 90° by a phase shifter 124. A summer 116 sums an output of the first summer 115 and an output of the phase shifter 124 to generate a complex signal I+jQ. A multiplier 117 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to each base station, and a signal separator 118 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 118 are filtered by lowpass filters 119 and 125, respectively, to generate bandwidth-limited signals. The output signals of the filters 119 and 125 are multiplied by carriers cos{2πfct} and sin{2πfct} in multipliers 120 and 126, respectively, to frequency shift the signals to a radio frequency (RF) band. A summer 127 sums the frequency-shifted I and Q channel signals.
FIG. 3B shows a structure of the conventional mobile station transmitter. Referring to FIG. 3B, multipliers 211, 221, 223 and 225 multiply a DPCCH signal and DPDCH1, DPDCH2 and DPDCH3 signals, which have undergone channel encoding and interleaving, by channelization codes Cch1, Cch2, Cch3 and Cch4, respectively, for spreading and channel separation. Orthogonal codes are used for the channelization codes. The output signals of the multipliers 211, 221, 223 and 225 are multiplied by gain coefficients G1, G2, G3 and G4 in multipliers 212, 222, 224 and 226, respectively. The gain coefficients G1, G2, G3 and G4 may have different values. The outputs of the multipliers 212 and 222 are summed by a first summer 213 and output as an I channel signal, and the outputs of the multipliers 224 and 226 are summed by a second summer 227 and output as a Q channel signal. The Q channel signal output from the second summer 227 is phase shifted by 90° in a phase shifter 228. A summer 214 sums the output of the first summer 213 and the output of the phase shifter 228 to generate a complex signal I+jQ. A multiplier 215 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to each base station, and a signal separator 229 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 229 are filtered by lowpass filters 216 and 230, respectively, to generate bandwidth-limited signals. The output signals of the filters 216 and 230 are multiplied by carriers cos{2πfct} and sin{2πfct} in multipliers 217 and 231, respectively, to frequency shift the signals to a radio frequency (RF) band. A summer 218 sums the frequency-shifted I and Q channel signals.
A conventional transmission signal structure of the base station and the mobile station will be made below. FIG. 5A shows how to transmit the downlink DPCCH and the uplink DPCCH when transmission of the uplink DPDCH is discontinued in a state where there is no data to transmit for a predetermined time.
FIG. 5B shows how to transmit the downlink DPCCH and the uplink DPCCH when transmission of the downlink DPDCH is discontinued in a state where there is no data to transmit for a predetermined time. As illustrated in FIGS. 5A and 5B, the mobile station constantly transmits the uplink DPCCH signal even when the DPDCH data is not existing in order to avoid a resync acquisition process in the base station. When there is no traffic data to transmit for a long time in the control-only substate, the base station and the mobile station make a transition to an RRC (Radio Resource Control) connection release state (not shown). In this state, transmission of the uplink DPDCH is discontinued, but the mobile station transmits pilot symbols and power control bits over the DPCCH until the transition is recoved, thereby increasing an interference of the uplink. The increase in interference of the uplink causes a decrease in the capacity of the uplink.
In the conventional method, although continuous transmission of the uplink DPCCH in the control-only substate is advantageous in that it is possible to avoid the sync reacquisition process in the base station, it creases an interference to the uplink, and decreases the capacity of the uplink. Further, in the downlink, continuous transmission of the uplink power control bits increases interference in the downlink and decreases the capacity of the downlink. Therefore, it is necessary to minimize a time required for the sync reacquisition process in the base station, decrease the interference due to transmission of the uplink DPCCH and decrease the interference due to transmission of the uplink power control bits over the downlink.